Equalizing repeating system



Dec. 30, 1947.

Filed Aug. 17, '1945 T. LINDENBERG, JR., ETAL EQUALIZING REPEATING SYSTEM 2 SheetEs-Sheet 1 SIGNAL OUTPUT FREQUENCY BY SAB W THEODORE INVENTORQ LINDENBERG JR T N. HOWELL ATTORNEYS @115 1947. YT. LINDENBERG, JR., ET AL 2,433,771

EQUALIZING REPEATING SYSTEM Filed Aug. 17, 1945 2 Sheets-Sheet 2 SELECTIVE 23 DEGENERATIVE 64 FEEQPBAGK 1 N VEN TOR.

THEODORE LINDENBERG JR.

BY SZ5ERT N. HOWELL ATTORNEYS Patented Dec. 30, 1947 UNITED STATES PATENT OFFICE EQUALIZING REPEATING SYSTEM Theodore Lindenberg, Jr., and Sabert N. Howell,

Manhasset, N. Y., assignors to Fairchild Camera and Instrument Corporation,

Jamaica,

17 Claims.

This invention relates to equalizing repeating systems and, while it is of general application, it is particularly suitable for use in universal equalizing amplifiers for wave-signal translating systems and apparatus, including sound responding, recording and reproducing circuits and apparatus, telephone lines and the like.

In audio-frequency signa1 responding, recording and reproducin systems, it often occurs that certain apparatus incorporated in the system or certain portions of the circuit itself have substantially non-linear frequency-response characteristics which, if uncompensated, introduce distortion into the output of the system. Furthermore, it frequently occurs that such audio-frequency systems must be used in conjunction with different signal-translating apparatus, for example different microphones, or different sound-reproducers, so that it is not possible to design the several components of the system to Work permanently with each other. It is an object of the invention, therefore, to provide a new and improved equalizing repeating system which is particularly useful as a universal component of audio-frequency systems of the type described, for compensating for, or matching, the non-linear frequency-response characteristic of one or more of the other components of the system.

It is another object of the invention to provide a new and improved equalizing repeating system by means of which the response at any particular frequency or any portion of the frequency range over which the system is to operate may be adjustably and selectively attenuated or amplified to a high degree with respect to that over the remainder of the frequency range.

In accordance with the invention, an equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of the frequency range comprises a signal input circuit, a signal output circuit, a first signaltranslating channel coupled between the input and output circuits and having a substantially constant repeating ratio over such frequency range, and a second signal-translating channel coupled between the input and output circuits and having a repeating ratio over such predetermined portion of the range substantially different from that over the remainder of the range. The system also includes means for adjusting the relative amplitudes of the signal outputs of the channels, as by adjusting the relative amplitudes of the signal inputs thereto, to maintain the sum of the signal outputs of the two channels approximately constant at frequencies over the remainder of the frequency range.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings while its scope will be pointed out in the appended claims.

Referring now to the drawings, Fig. 1 is a circuit diagram of an equalizing repeating system embodying the invention; Fig. 2 is a graph illustrating certain operating characteristics of the system of Fig. 1 to aid in the understanding of the invention; while Fig. 3 is a circuit diagram of a modified system having operating characteristics similar to those of Fig. 1.

Referring now to Fig. 1 of the drawings, there is represented an equalizing repeating or amplifying system for translating wave signals within a given frequency range with an adjustable repeating ratio or gain over a predetermined portion of the frequency range, for example with an adjustable peaked response, either positive or negative, at a predetermined frequency of the range. This system comprises a signal-input circuit having terminals ID, ID and a signal-output circuit having terminals l I, l I. A first signaltranslating channel is coupled between the input circuit l0 and the output-circuit H including a vacuum tube I2 of any suitable type and the channel including the tube I2 is designed to have a substantially constant repeating ratio or gain over the entire frequency range. The signal-input electrode or grid of the tube I2 is connected to the input circuit I0 through a voltage-divider network to be described hereinafter and an isolating resistor l3. The tube I2 is also provided with a suitable grid-return resistor I4 and a cathode-bias resistor l5. Space current is supplied to the anode of the tube 12 through a load resistor l6 from a suitable source +B, as indicated. The anode of the tube I2 is coupled to the output circuit H through a blocking condenser [1.

The equalizing system of Fig. 1 also includes a second signal-translating channel coupled between the input circuit 10 and the output circuit l I and including a plurality of vacuum tubes, for example three tubes l8, l9 and 20 coupled in cascade and designed to have a repeating ratio or gain over such predetermined portion of the frequency range substantially different from that over the remainder of the range. For example, the second channel may be designed to have a peaked response at said predetermined frequency plied to the tube 18 through a load resistor;

from a suitable source +B, as indicateQ 'The anode of the tube I8 is coupled to the signalinput electrode to the second tube l9 through a coupling condenser 21 and a grid resistor 28, the tube l9 being provided with 'a cathode-bias re= The equalizing repeating system of the invention also includes means for adjusting the relative amplitudes and polarities of the signal outputs of the two channels to maintain the sum thereof approximately constant at the frequencies over such remainder of the frequency range. This means is preferably in thief (arm of 'iiiearis interposed between the input circuit In and the two channels for adjusting the relative amplitudes andpolarities of the signal inputs to the channels to maintain the sum of the signal outputs over the remainder of the frequency range constant. gfial-input circuit Iii may be connected to a pr ary winding 58a of a transformer 50 havinga secondary winding 50b, the midpoint of which is grounded to provide the signal-input circuit with an intermediate point sistor 29 and being supplied with space'current through a load resistor 30 from a suitable source +B, as indicated. Similarly, theanode of the tube [9 is coupled to the signal-input electrode of the third tube 2|] throughfa'couplir'ig condenser 31 and a grid resistor 32, the cathodeof the tube 20 being provided with'a bias resistor 33 and the anode of the tube zil being provide'd with space current through a resistor 34 in parallel with a load circuit comprising a blocking condenser 35 and resistors 35 and 37 in series. I

If desired, the anode of the tube 20 may be connected in parallel with the anode of the tube l2 in the first channel to translate the signal to the output circuit ll. However, it is preferable, as shown, to utilizean auxiliary isolating tube 38 having its control electrode'connected in parallel with the control electrode of the tube20 and having its anode connected in parallel with the anode of the tube l2, so that it is supplied with space current from the source +B through the common load resistor 16. The tube 38 may be provided with a suitable cathode bias resistor '39. The tubes l2 and 38 should have identical electrical characteristics. i

The described characteristics may be imparted to the second charmel including thetubes 18, I9, 20 and 38 by designing it to have a normal gain substantially greater than th'ato'f the first channel, which it normally does have byvirtueof its cascade-coupled vacuum-tube amplifiers, but including means for reducing the gain thereof over the remainder of the frequency range. This means may take the form of a degenerative feedback circuit 40 coupledbetween the load resistor 31, and thus to the outputelectrode of the third vacuum tube 20, and the grid resistor '23, and thus to the input electrode of the first vacuum tube Hi. The feedback circuit is designed to be unresponsive at the predetermined portion of the frequency range over which an adjustable repeating ratio is desired. The feedback circuit lfi may be of any conventional type havin if e desiredfrequency-response characteristic but there is illustrated by way of example a feedback network comprising adouble-T resistance-capacitance bridge designed to resonate at the predetermined frequency at which the peaked response is desired. "Specifically, thenetwor'klt comprises a first T including series capacit'ancearms 4i and d2 and a shunt resistance arm comprising a fixed resistor '43 in series with an adjustable resistor 44, The second T of the network includes seriesresistance arms comprisingrespectively, an adjustable'resist'or in series with the fixed resist'orjii and an adjustable resistor 41 in series with the fixed resistor 48, and a shunt-capaci- '54 'are so pro erties the several p'oiiits 1:

gain as of tiles on" substantially infi of reference potential. Voltage divider means are connected across the input circuit, specifically a pair of voltage ivi ers eifectively in parallel across the secondary i ding 5513." he "of the voltage'dividers 5| 'ispo nnectedbetw n thfe'up per terminal of the windifigfifib ai r d. igrouncl,while the sec v ia f. l irziisfipll ei fb the secondary windin through fixedlresi'stors 53 and 54. 'I'he voltage dividers 51 and 52-are provided with adjustable eehtatts 51d and 52a, respectively, which are initlividuailly -eehhee'tee to the signal input elect ae 'ofthe tubes l2 alnd' l 8 in the two signal-{lira latii ifg' ehahheie. The ad'- J'ustable contacts "5T ndEZa areconiiecteii bye unicontrol mechanism indicated schematically by the dbt-daSh-lih'ii ior 5 simultanebusly adjusting the contacts inop'posite potentia sen es and, as explained herei arter,reredjusti g ehiy one of the contacts, namely the chili-fact 5 2a,-throiigh the point or reference potential {during t e ad justmn't or the contact 511 yer its respective range. As indicated schematically, the vintage dividers 51 and 52 are preferably logarithmically tapered or shap'e'dlso that the contacts 5| 2i ah d52'a have a linear gaiii adjustmentcharacteristicon a decibel scale; I 7 7' In 'eilzplainin'g the "operation of the systin'of Fig.'1,'d'escrib'ed abet-e111; will be assumedth'eit the adjustable cohtactstlaand sza' readjustable between their 'lifiiitiligdbtfd l'lh alliifibt dash-line positiohsas represented. 1-ti"sa1 seaesumed that the constants erthevmtage divider resistors 5| ends: "ahdfli resistors 533E116 he1petentia1e a pearin at the limiting arid mm; positions "er the adjustable-contacts? maha'tze have-t ereiative values indicated bri the ve1tege a wiuereet ofthe first' chaiir el the range 'to 'be tr is 100. It also ssu so proportionedlas to second channel over equal to that e'rthe' rst"ehefr1he1. Atthefresei hit; 1; ith'the'fo'iegoih'g assumptions and'vvith'the on'd channel isn'ot but has its normal ga adjustable contacts 5m and 52a in their dottedline positions, it is seen that no signal is applied to the first signal channel so that its output will be zero. At the same time, one unit of the signal is applied to the second channel which, with a gain ,u.3 of 100, would result in an output signal of 100 units at the predetermined frequency at which the degenerative network iii is resonant. However, due to the loading of the inactive vacuum tube Hi, this signal output as impressed upon the output circuit ii is reduced to 50 units. Over the remainder of the frequency range the degenerative network iii reduces the gain of the second channel to so that its signal output is 10 units, which is reduced by the loading of the tube l2 to 5 units. ihe resulting characteristic of the system with the contacts Eiia and 52a in this position is represented by Curve A of Fig. 2 in which the ordinates represent signal output on a logarithmic scale and the abscissae represent frequency on a linear scale. It will be understood that the sharpness of the response at the frequency in may be adjusted within wide limits by the proper design of the degenerative network Gil.

Assume now that the adjustable contacts 51a and 52a occupy their intermediate solid-line positions. Under these conditions, one unit of signal input is applied to the first channel which, increased by the gain of 10 of this channel and reduced by the loading of the parallel tube 38, results in a signal output of 5 units over the entire frequency range. At the same time, the signal input to the second channel is zero so that it produces no signal output and the total output of the system is that of the first channel and is represented by Curve B of Fig. 2. Obviously for positions of the adjustable contacts Sta and 52a intermediate the two positions just described, a series of curves intermediate Curves A and B will represent the overall response characteristics of the system.

If new the adjustable contacts em and 52a are moved to their lower dot-dash-line positions, it is seen that a signal of 1.10 units is applied to the first channel including the tube l2 and that a negative signal input of 0.10 unit is applied to the second channel. Considering the first action at the frequency in, the signal output of the first channel is 11 units which is reduced by the loading of the tube 38 to 5.5 units. At the same time, the signal output of the second channel is 10 units which is reduced by the loading of the tube ii! to a 5.0 units so that the resultant signal output at the frequency in is 0.5 signal units. Over the remainder of the frequency range, the signal output of the first channel is likewise 5.5 units, while the signal output of the second channel is 1 unit which is decreased by the loading of the tube 12 to 0.5 unit so that the resultant signal output of the system is 5.0 units. This is represented by Curve 0 of Fig. 2. Obviously, for positions of adjustable contacts 53a and 52a intermediate the last two positions described, there results a series of curves intermediate Curves B and C.

Thus it is seen that, by the use of the equalizing system of the invention, there is procured a resultant repeating ratio or gain which has a peaked response at a predetermined frequency it within the range which is adjustable between maximum and minimum values, while the repeating ratio or gain over the remainder of the fre- 6 quency range is maintained substantially constant. It will be apparent that, by simultaneously and appropriately adjusting certain elements of the degenerative feedback network 4%], for example resistors 14, 45 and M, the frequency of resonance f0 of the network it may be shifted over a wide range within the operating frequency range of the system. By a combination of the adjustment of the resonant frequency of the network 49 and of the adjustable contacts 51a. and 52a, a wide variety of overall-response characteristics may be obtained which are capable of compensating for, or matching, the non-linearresponse characteristics of a wide variety of sound-translating apparatus.

By the use of the logarithmically tapered voltage dividers 5! and 52, the adjustable contacts 51a and 52a produce a linear variation in the peaked response of the system on a decibel scale. This is represented in Fig. 2 in which the maximum emphasis at the frequency in is +20 decibels, while the maximum attenuation is 20 decibels. In general, if the adjustable contact 5la is adjustable over the range 0-p1-p2 while the contact 52a is simultaneously adjustable over the signal potential range p3-O(p4), representing the three positions of these contacts illustrated in the drawing, and the circuit constants of the system are proportioned to satisfy the relations:

(P2 7 1) #1 Pile 1 1m Pun-Pil s the repeating ratio is maintained constant over the remainder of the frequency range while it is adjustable over the predetermined portion of the frequency range by equal amounts, in decibels, above and below that of the remainder of the range.

Referring now to Fig. 3, there is represented a modified equalizing repeating system in which several of the component elements are the same in construction and operation as those of Fig. l and are identified by the same reference numerals. In the system of Fig. 3, the adjustable voltage divider 52 is replaced by a fixed voltage divider 60 having terminals 60a and 651) at the points of signal potential corresponding to the limiting positions of the adjustable contact 52a of Fig. 1. The potentials of these two points are selectively applied to the second channel by means of aswitch 5| having contacts ii la and 6 lb connected to the points 68 a and 56b, respectively, and extending over a range equal to the range of adjustment of the adjustable contact cm. In this modification, the second tube Q9 of Fig. l is replaced by a cathode-follower tube 62 having a cathode-biasing circuit 53 and a cathode-load resistor 64 which is coupled through a condenser 65 and the selective degenerative feedback network Ml to the grid resistor 23 in the input circuit of the tube l8. With this arrangement, as is well known, the signal is not reversed in polarity at the output circuit of the tube 62 so that, if the system is designed with adequate gain, only two rather than three tubes need be provided in the second channel.

In the arrangement of Fig. 3, the adjustment of the signal output potential of the second channel is effected by a pair of voltage dividers $5 and 66 interposed in parallel in the second channel, as

at the output circuit of tube l8 through a coupling condenser 61. The voltage dividers have a i common adjustabl contact 68 disposed selectively to engage the dividers 65 and 66 and connected to the signal-input electrode of the isolating tube 38. There is provided a unicontrol mechanism, represented schematically by the dotdash-line 59, for simultaneously actuating the adjustable contacts 5M and 68 and the switch iii. The switch 6| derives from the input circuit and applies to the second channel signals of predetermined different values and opposite plarities for different portions of the range of adjustment of the contact Ia, while the adjustablecontact 63 selectively engages the voltage dividers 65 and 66 in accordance with the polarity of the signal applied to the second channel.

The principles of operation of the system of Fig. 3 are entirely similar to those of the system of Fig. 1, the adjustment of the signal outi put of the second channel being effected by means of the voltage dividers 55 and 66 at an intermediate point in the channel, rather than by the voltage divider 52 of Fig. 1 at the input of the channel. The contacts Sta and 61b are effec-- tively cross-connected to the contacts 60a and. 6%, respectively, to take into consideration the reversal of the polarity of the signal output of the tube I 8 with respect to the signal input to the second channel.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without dea predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating ratio over said frequency range, a second signal-translating channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a repeating ratio over said predetermined portion of said range substantially different from that over the re! mainder of said range, and means for adjusting the relative amplitudes of the signal outputs of said channels in opposite senses to maintain the sum thereof approximately constant at fre-- quencies over said remainder of said frequency range.

2. An equalizing amplifying system for translating wave signals within a given frequency range with an adjustable gain over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output cir- 1 uit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant gain over said fre quency range, a second signal-translating channel coupled between said input and output cirv suits in aiding phase with respect to said first channel and having a gain over said predetermined portion of said range substantially different from that over the remainder of said range. and means for adjusting the relative amplitudes of the signal outputs of said channels in opposite senses to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range.

' 3. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating ratio over said frequency range, a second signal-translating 'channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a repeating ratio over said predetermined portion of said range substantially different from that over the remainder of said range and having a repeating ratio over said remainder of said range substantially equal to that of said first channel, and means for adjusting the relative amplitudes of the signal outputs of said channels in opposite senses to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range.

4. An equalizing repeating system for translating Wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating ratio over said frequency range, a second signal-translating channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a repeating ratio over said predetermined portion of said range substantially different from that over the remainder of said range, and means for adjusting the relative amplitudes and polarities of the signal outputs of said channels in opposite senses to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range.

5. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating ratio over said frequency range, a second signaltranslating channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a repeating ratio over said predetermined portion of said range substantially different from that over the remainder of said range, and means for adjusting the relative amplitudes of the signal inputs of said channels in opposite senses to maintain the sum of the signal outputs thereof approximately constant at frequencies over said remainder of said frequency range.

6. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable peaked response at a predetermined frequency'of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating ratio over said frequency range, a second signal-translating channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a peaked responseat said predetermined'frequency, and means for adjusting the relative amplitudes of the signal outputs of'said channelsin' opposite senses to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range.

'7. An equalizing amplifying system for translating wave signals within a given frequency range with an adjustable gain'over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits including a vacuum tube and having a substantially constant gain over said frequency range, a second signaltranslating channel coupled between said input and output circuits in aiding phase with respect to said first channel and including a plurality of vacuum tubes in cascade and having a normal gain substantially greater than that of said first channel but including means for reducing the gain thereof over the remainder of said frequency range, and means for adjusting the relative amplitudes of the signal outputs of said channels in opposite senses to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range.

8. An equalizing amplifying system for translating wave signals Within a given frequency range with an adjustable gain over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits including a vacuum tube and having a substantially constant gain over said frequency range, a second signal translating channel coupled between said input and output circuits in aiding phase with respect to said first channel and including a plurality of vacuum tubes in cascade and having a normal gain substantially greater than that of said first channel but including degenerative feedback means unresponsive at said predetermined portion of said frequency range, and means for adjusting the relative amplitudes of the signal outputs of said channels in opposite senses to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range.

9. An equalizing amplifying system for trans lating wave signals within a given frequency range with an adjustable gain over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits including a vac uum tube and having a substantially constant gain over said frequency range, a second signaltranslating channel coupled between said input and output circuits in aiding phase with respect to said first channel and including three vacuum tubes in cascade and having a normal gain substantially greater than that of said first channel but including degenerative feedback means coupled from the output electrode of the third of said tubes to the input electrode of the first thereof, said feedback means being unresponsive at said predetermined portion of said frequency range, and means for adjusting the relative amplitudes of the signal outputs of said channels in opposite senses to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range.

10. An equalizing amplifying system for translating wave signals within a given frequency range with an adjustable gain over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits including a vacuum tube and having a substantially constant gain over said frequency range, a second signaltranslating channel coupled between said input and output circuits in aiding phase with respect to said first channel and including a plurality of vacuum tubes in cascade andhaving a normal gain substantially greater than that of said first channel but including degenerative feedback circuit including a double-T resistance-capacitance bridge resonant at a frequency in said predetermined portion of said frequency range, and means for adjusting the relative amplitudes of the signal outputs of said channels in opposite senses to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range.

11. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion'of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating. ratio over said frequency range, a second signal-translating channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a repeating ratio over said predetermined portion of said range substantially different from that over the remainder of said range, and means interposed between said input circuit and said channels for adjusting the relative amplitudes of the signal inputs to said channels in opposite senses to maintain the sum of the signal outputs thereof approximately constant at frequencies over said remainder of said frequency range.

12. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and outputcircuits-andhaving a substantially constant repeating ratio over said frequency range, a second signal-translating channel coupled between said input and output circuitsin aiding phase with respect to said first channel and having a repeating ratio over said predetermined portion of said range substantially different from that over the remainder of said range, and voltage-divider means connected across said input circuit and including a pair of adjustable contacts individually connected to said channels for adjusting the relative amplitudes of the signal inputs to said channels in opposite senses to maintain the sum of the signal outputs thereof approximately constant at frequencies over said remainder of said frequency range.

13. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signalinput circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating ratio over I said frequency-range, a second signal-translating channel coupled between said input and output circuits in aiding phase with respect to said first parallel across said input circuit, each having an adjustable contact, said contacts being individually connected to said two channels, and means for adjusting said contactsin opposite potential senses for adjusting the relative amplitudes of a the signal inputs to said channels to maintain the sum of the signal outputs thereof approximately constant at frequencies over said remainder of said frequency range. v

14. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signal input circuit having an intermediate point of reference potential, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating ratio over said frequencyranga'a second signaltranslating channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a repeating ratio over said predetermined portion of said range substantially different from that over the remainder of said range, a pair 'of voltage dividers connected in parallel across said input circuit, each having an adjustable contact, said contacts being individually connected to said two channels, and means foradjusting said contacts in opposite potential senses and for adjusting only one of said contacts through said point of reference potential for adjusting the relative amplitudes and polarities of the signal inputs to said channels to, maintain the sum of the signal outputs thereof approximately constant at frequencies over said remainder of said frequency range.

15. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and hav-& ing a substantially constant repeating ratio 4 over said frequency range, a second signal-translating channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a repeating ratio #3 over said predetermined portion of said range substantially difierent from that over the remainder of said range and having a repeating ratio 2 oversaid remainder of said range, a pair of voltage dividers connected in parallel across said input circuit, each having an adjustable contact, a first of said contacts being connected to said first channel and being adjustable over a signal potential range -p1p2 and the satisfy the relations:

1 114: Pal

(Pa-P1) I 1 1 41 2 1 31 35 Pil 2 1m Pu l-Pil s whereby the, repeatin ratio of the system is maintained constantover said remainder of said range and the repeating ratio over said predetermined portion of said range is adjustable by equal amounts, in decibels, above and below that over said remainder of said range.

16. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit, a first signal-translating channel coupled between said input and output circuits and having a substantially constant repeating ratio over said frequency range, a second signaltranslating channel coupled between said input and output circuits in aiding phase with respect to said first channel and having a repeating ratio over said predetermined portion of said range substantially different from that over the remainder of said range, and means for adjusting the relative amplitudes of the signal outputs of said channels to maintain the sum thereof approximately constant at frequencies over said remainder of said frequency range comprising a voltage divider connected across said input circuit having an adjustable contact connected to said first channel, switch means for deriving from said input circuit and applying to said second channel signals of predetermined different values and opposite polarities for different portions of the range of adjustment of said contact, a pair of voltage dividers interposed in parallel in said second channel and having a common adjustable contact disposed selectively to engage said pair'of dividers in accordance with the polarity of the signal appliedto said second channel, and um'control 'meansfor actuating said adjustable contacts and said switch means in unison.

17. An equalizing repeating system for translating wave signals within a given frequency range with an adjustable repeating ratio over a predetermined portion of said frequency range comprising, a signal input circuit, a signal output circuit; a first signal-translating channel coupled between said input and output circuits 7 including a single vacuum tube and having a substantially'constant repeating ratio over said frequency, range, a second signal-translating channel coupled between said input and output circuits in aiding phase with respect to said first channel and including two vacuum tubes the second of which has a cathode load circuit, said second channel havinga normal gain substantially greater than that of said first channel but including degenerative feedback ,means coupled from said cathode load circuit to the input electrode of the first tube thereof, said feedback means being unresponsive at said predetermined portion of said frequency range.

THEODORE LINDENBERG, JR. 1

SABERT N. HOWELL.

REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS,

Muflly Feb. 27, 1945 

